The election in Greece is being closely watched by financial markets, nervous that a Syriza victory might trigger a standoff with the country's European Union and IMF lenders and spark a new financial crisis that could push it out of the euro zone.
A Rass survey conducted between Jan. 14 and 15 for the Ependysi newspaper showed Alexis Tsipras' Syriza party leading by 3.8 percentage points over Samaras' New Democracy conservatives, up from 3 points in a previous poll by the same pollster.
The poll put support for Syriza, which has promised to cancel austerity measures and renegotiate the country's debt, at 29.6 percent against 25.8 percent for New Democracy, nine days before the vote.
Another survey by Metron Analysis, to be published in Parapolitika newspaper on Saturday, showed Syriza widening its lead to 4.6 percentage points from 4.1 points earlier this month.
Syriza would get 35.4 percent of the vote versus 30.8 percent for New Democracy, the poll showed.
The centrist party To Potami (River) ranked third in both surveys.
The leading party must generally receive between 36 and 40 percent of the vote to win outright, though the exact threshold depends on the share of the vote taken by parties that fail to reach a 3 percent threshold to enter parliament.
The electoral system automatically gives the winning party an extra 50 seats to make it easier to form a government.
Syriza would get 147 of the 300 seats in parliament, the Metron Analysis poll showed, falling short of an overall majority. New Democracy would get 85 seats.